This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The most common cause of morbidity and mortality in patients with Cystic Fibrosis (CF) is pulmonary system failure caused by Pseudomonas aeruginosa infection. One potential mechanism of P. aeruginosa damage to the lung is destruction of lung surfactant. Surfactant dysfunction can lead to small airway closure and severely decreased lung function. While the clinical significance of surfactant dysfunction in the CF lung is not fully understood, surfactant dysfunction may result in reduced lung function during exacerbations. We propose that several virulence factors secreted by P. aeruginosa function to degrade surfactant during infection resulting in decreased lung function. Preliminary evidence from a mouse lung infection model shows that P. aeruginosa infected mice show extensive airway closure. Some of this closure is due to the secreted hemolytic phospholipase C, PlcH, but in a plcH deletion strain there remains significant surfactant dysfunction. It is our hypothesis that the secreted lipase encoded by PA4921 is one of the additional mediators of surfactant degradation during P. aeruginosa lung infection. In this study we will verify the predicted enzymatic activity of PA4921 and determine the transcriptional regulatory mechanism governing its induction in pulmonary surfactant. Following the initial characterization, we will examine the role of PA4921 in alteration of lung mechanics in both wild type and Cystic Fibrosis Transmembrane Regulator knock-out (CFTR KO) mice. Lung mechanics, surfactant composition, and surfactant function will be measured during P. aeruginosa infection. Pulmonary instillation of purified PA4921 enzyme will be tested for sufficiency to alter lung mechanics and catalyze surfactant degradation. These experiments will allow us to determine if PA4921 is a potential therapeutic target applicable to CF exacerbations